Internal rechargeable battery; compatible with Windows operating systems
Customer Reviews:
Decent but not sufficient - why I returned it 
I got this player for long plane trips after much research. I was torn between this and the Archos 605. I went with this one because it supported lots of formats. I ended up returning it, and am waiting for something better to come out.
Here are the problems I had with it, in decreasing order of importance:
1. It says it supports lots of doc formats like word, excel, and pdf. In actuality, the only formats it natively supports is text and csd. it provides software (windows only) to transcode to csd. The kicker is that apparently the software requires that you have installed the program controlling the format to transfer from. E.g., to convert an excel doc, you need to have microsoft excel installed. Ugh. I feel deceived. Further, I wasn’t impressed with the csd viewing capabilities.
2. Frustrated, I converted some files to text and tried them out. The player has some bugs where it only display portions of the text file! Somehow they managed to mess up the text viewer on the player so it only displays a small prefix of the text file.
3. On video files I was watching, it has a bug in which the audio is 5 seconds behind the video - wow did that give me a headache.
4. The radio reception on the device sucks, and the auto-record does not support once-a-week recording.
5. The video player has a bug where if you fastforward twice in succession, the player locks up.
6. It was clunky to forward and rewind thru video. You have to go thru a bunch of menus to specify how much to forward and rewind, and it doesn’t display images during forward/rewind so it’s hard to tell if you’ve skipped over the spot you wanted to fastforward to.
7. On the plane, with a pair of Sennheiser HD-280 headphones, I found myself wishing the volume control would go louder.
On the plus side, it was easy to connect to Mac and Linux boxes. It just appears as a USB drive, which was nice.
I don’t like the Archos player because of the nickle-and-diming of extra features and limited format support. so I think I’m just going to sit out of the market until something more compelling comes along.
Best Portable Video Player! 
I have owned the Archos 605 WiFi which is a great PMP (Portable Multimedia Player). It plays videos, music, can go online and has a touch screen interface, but what it lacks is the amount of formats it supports. It is limited and you are required to purchase plug ins to access more formats and even then it’s pretty much limited. Now comes a player that solves this problem and that is the Cowon A3. The A3 can play everything the Archos 605 can plus way more extra formats. It supports MKV which no other player supports (I’m throwing that out since a lot of my videos are in MKV) The screen is huge for viewing videos and the audio can be configured. Battery life is good for video (estimated 7 hours) but audio is not so great (9 hours) though I have a feeling you can get more out of it if you lowered the brightness of the LCD screen and the power saver mode to 10 sec. One key factor is it can play HD resolution (720p only) which no other player can do. Here are my few gripes (hoping that future firmware updates will take care of them, though a few are physical traits and nothing can be done)
1. No native H.264 support (a lot of my video files are in H.264 and this is something that will probably be resolved through a firmware update)
2. No touch screen interface! Using the stick can be annoying at times especially when you want it to go down but you press down on it instead.
3. Fingerprints! The Archos 605 had plastic buttons which did not smudge, whereas the A3 smudges easily.
4. No pouch included.
Even with these inconveniences, the A3 easily surpasses the Archo 605 because of the amount of formats it supports and the battery life is much higher. Also, one important factor, the charge time is much less since the Archos 605 does not include an AC adapter and only USB Charging. Charge time is 5 hours (A3) vs. 10 hours (Archos 605).
Of course I only mentioned the Archos 605 but this player easily bests the following popular players: iTouch/iPods, Creative Zen Vision W, and the iRiver. I highly recommend this for those who are into watching video, though not recommended for listening to music because of the battery life (there are cheaper and better alternative options for just music and iAudio 7 happens to be one of them)
Note: This is not a final rating as I am waiting for firmware updates and the score will change according to those updates.
Update: I still stand by when I said that there is no native H.264 support (though there was a firmware update recently it has not resolved the problems for playing the format) Once this is resolved I will post it up
Update 03/19/08: A new firmware update was just released and it improves on the following: extended music playing hours from 9 to 13 hours, improved avi playing, improved subtitles being displayed (there are a lot more but these are the major improvements that I find noteworthy) What it’s still missing is being able to play H.264, specifically with MKV. There are no improvements from the last time as only a very few MKV. files work on the player and even the files that work with the player suffers from bad frame rate. Hopefully the next firmware will fix the biggest problem with this player, MKV. support and improvement with the H.264 One thing to add, I am glad they fixed the avi as it plays much better this time around.